The singer dropped a pap shot of them together in a car on her IG Stories Sunday, and called out the irony of Paul crying harassment during that moment ... when she says he welcomed the attention himself.

In the pic it looks like they're getting hassled -- Paul's got his arm up in the car, trying to shield himself from the pap cameras, while Britney's crouching all the way down next to him.

But, Britney says things played out differently IRL ... writing in the caption, "Why was he going 90 in a neighborhood with one pap following only to roll the window down when the pap pulls to the side of me ????."

She continued, "Then he calls his mom and says he's being harassed. Why did he roll the window down with me crying in the seat??"

Britney also shared a cryptic quote, which read, "Her attitude is savage, but her heart is gold" ... before declaring in a since-deleted caption, "I will never be with another man as long as I live!!!"

As we know ... Britney's brief relationship with Paul after splitting from husband Sam Asghari has been rocky from the start.

TMZ broke the story in April ... Britney and Soliz got into a physical fight after a night of drinking at the Chateau Marmont on the Sunset Strip -- and an ambulance was also called because Britney hurt her ankle.